1. Field of the Invention
This invention relates to welding apparatus and a method for welding on an end face of a work-piece with a circular opening and in particular to such welding apparatus which is mounted onto the end of the work-piece and rotates about the projected axis of the opening to generate a spiral weld bead. The invention has particular application to such apparatus and method which utilizes gas tungsten arc welding--hot wire welding equipment with an arrangement for connecting electrical, gas and cooling water leads and conduits to the rotating equipment.
2. Background of Information
There are situations where it is necessary to apply a coating of weld material, often referred to as "buttering", to a work-piece for welding to another work-piece. At times, it can be very awkward to apply such a weld. For instance, such a weld is used on a steam generator in a nuclear power plant. The large stainless steel piping running from the nuclear reactor is welded to the steam generator at a channel head nozzle. Since the steam generator is manufactured primarily from low alloy steel, the nozzle face must be buttered with a non-ferrous material to provide a weldable interface to the piping.
Current practice is to butter the low alloy steel nozzle of the steam generator with nickel alloy weld metal and then to weld it to a forged stainless steel safe end. The safe end becomes the interface to the field piping. The gas tungsten arc welding--hot wire process (GTAW-HW) is used because of its good deposition rate, stable arc characteristics, and high quality weld deposits using nickel alloy filler metals. Typically, the nozzles have been buttered using existing GTAW-HW equipment mounted on a large manipulator. The steam generator channel head is semi-spherical with the nozzle positioned asymmetrically. The channel head is mounted on a welding positioner with the nozzle facing upward and rotated about the central axis of the nozzle. This places the nozzle about 20 feet above floor level. The welder is supported above the rotating nozzle. This procedure results in long set-up times, welding operator discomfort, and weld concentricity problems. Only manual adjustments are available for regulating travel speed and weld bead spacing to compensate for radius changes. Both the speed and bead placement are readjusted for the next bead at the end of each rotation. These adjustments result in numerous starts and stops within the weld deposit. The resulting weld quality of the typically 10 bead wide by 14 layer high deposit is less than process capabilities.
There is a need for an approved apparatus and method for buttering the end faces of parts having circular openings such as the nozzles on steam generator channel heads.
In particular, there is a need for such apparatus and method which can make continuous welds of this type.
There is a further need for such apparatus and method which produces a continuous weld which is concentric with the opening.
There is also a need for such apparatus and method which uses the GTAW-HW process and accommodates the numerous conduits and electrical leads needed for that process.